When shard has more than 10k ranges we currently degrade new locks into full shard locks. However it's possible that some particularly long transactions acquire a lot of locks and cause faster newer transactions to conflict en masse, when they don't really conflict. There's an idea, that we could instead change oldest / largest locks into whole shard locks, freeing up space in the range tree for new locks, and allowing transactions with a small number of locks to run unimpeded.